1. Field of the Invention
The present invention relates to a photodosimeter film badge and, more particularly, to a film badge and a method of making same for use in measuring irradiance during phototherapy for the treatment of hyperbilirubinemia.
2. Description of the Prior Art
Bilirubin is a molecule that is normally found in the blood. It is formed from the hemoglobin of red cells in the course of their normal breadknow and is transported in the plasma to the liver where it is conjugated with glucuronic acid to form bilirubin diglucuronide and excreted by way of the bile into the intestines. However, when the liver is not fully functional in this respect, as often occurs in the first few days of an infant's life, especially in premature infants, the bilirubin level can rise in the blood serum and lead to jaundice, which is distinguished by a visually detectable yellow coloration of the skin. The medical term for this condition, too much bilirubin in the blood, is hyperbilirubinemia.
If allowed to persist at high levels in the blood, the bilirubin can cross the blood-brain barrier and stain the brain cells with resulting permanent neurological damage. The condition is known as kernicterus and results in various degrees of motor and mental retardation.
Fortunately, bilirubin can be bleached by light and the photoproducts of bilirubin are excretable. Furthermore, the bilirubin reaction to light is apparently neither photoreversible nor chemically reversible in the dark. In addition, the photoproducts of bilirubin are apparently incapable of crossing the blood-brain barrier, being water soluble, and are also apparently non-toxic.
The discovery of the bilirubin photoeffect has resulted in the use of phototherapy for the treatment of hyperbilirubinemia becoming a generally accepted therapeutic practice. Many carefully controlled studies have been published and all have found that phototherapy is effective in lowering serum bilirubin levels. One can achieve 30 to 50 % lower average serum bilirubin concentrations in light treated infants as compared to other methods of control.
In spite of the demonstrated effectiveness of phototherapy in decreasing serum bilirubin concentrations in neonatal infants and the associated prevention of death or injury to the central nervous system, a concern has recently developed due to the lack of knowledge of the safety and efficacy of the use of light energy in the treatment of human disease. For example, there is no direct evidence available that answers the question whether light-induced reductions in serum bilirubin concentration during neonatal life will decrease the risk of later neurologic and psychologic defects that are believed to be the sequelae of hyperbilirubinemia. There is presently a large deficit in knowledge of the nature of the photodegradation products of bilirubin, possible photosensitizing and photoallergic reactions involving endogenous biologic substances or prenatally or neonatally administered drugs, potential genetic and carcinogenic hazards of phototherapy in human infants, long term untold psychologic, endocrine or cellular changes that may result from phototherapy, the most effective wavelength for phototherapy, and the most effective intensities and exposure times.
These concerns have lead to a demonstrated need for a measurement technique capable of responding to the total exposure of the newborn baby to light within the spectral region effective in the photodecomposition of bilirubin. With such a measurement technique, meaningful data can be accumulated.
Some of the fluorescent lamps used in phototherapy units emit electromagnetic radiation in ranges that extend beyond the limits of the visible spectrum. Others emit radiation in more restrictive ranges. Yet, it is common practice for exposures during phototherapy to be measured with light meters. However, light meters are inappropriate for this purpose because they are designed to measure illuminance, that is, the density of electromagnetic radiation spectrally weighted to the response of the human eye. Accordingly, they function with maximum sensitivity between 500 and 600 nanometers (nm) and only with diminishing sensitivity down to 400 nm. Unfortunately, this spectrum does not coincide with the action spectrum for the phototherapy of hyperbilirubinemia. Available data on the action spectrum for photodegradation of serum bilirubin shows that light having a wavelength of 425-500 nm is most effective for bleaching serum bilirubin. Therefore, standard light meters are inadequate for present purposes.
Only a spectroradiometer can provide the desired radiometric information, namely spectral irradiance, which is the radiative power density of the incident light, expressed in watts/square centimeter/unit wavelength, over the entire spectral range incident on the patient. Unfortunately, spectroradiometers are complex, expensive, and probably unsuited for use in a nursery.
A practical instrument for monotoring phototherapy in a hospital environment must be capable of meeting certain tests. First of all, the instrument and essential accessories should be inexpensive enough to ensure their use in conjunction with phototherapy that is conducted under any and all circumstances. Operation of the equipment should be simple enough for nursery personnel to become skilled in its use after a short instruction period. The equipment should be susceptible to routine, simple calibration within the hospital nursery. The sensing element must be small enough so that it will not interfere with the care of the infant and must be constructed so that it will not be damaged by sterilization.
From a technical standpoint, certain additional criteria are also essential. The action spectrum for the sensing element must match the action spectrum for the photodestruction of serum bilirubin in a neonatal infant, i.e. the sensing element must respond in exactly the same region of the spectrum as that which is effective in the photodecomposition of bilirubin. Furthermore, the kinetics of the change in the sensing element must match the kinetics of the change in bilirubin levels during photodecomposition. The sensing element must be responsive to the phototherapy irradiance over periods of phototherapy extending from a few hours to approximately 96 hours (4 days). Finally, any measurement technique should require a minimum of handling or processing to make a measurement. Preferably, the equipment should be directly processed and not such that chemical processing is required. Only in this way will the equipment permit continued monitoring of total exposure without requiring constant recalibration or restarting of the process.
Many commercial radiometers are available at prices ranging from several hundred to several thousand dollars. They have a wide variety of sensors, spectral ranges, calibration capabilities, etc. However, as presently offered by existing manufacturers, none meets all the criteria listed above.